The invention relates generally to extendable surfaces for supporting people and material for movement between two structures at a height. More specifically, the invention relates to extendable platforms or ramps to assist loading and unloading boats and vehicles, and, more particularly, but not by way of limitation, it relates to an improved extendable gangplank for use in combination with a pontoon-type barge or boat.
Ramps are in common use for loading and unloading vehicles, by providing a smooth transition from vehicle to the loading area. Examples of ramp use are, for example, ramps used by furniture movers to enable them to easily move a piece of furniture from the ground to the truck body, which is usually several feet above the ground. Ramps are also used as gangplanks in the boating industry to allow personnel to move from the shore or dock to a boat without getting wet. The ramp is usually stored in the body of the vehicle or underneath its floor when it is no longer required. Such ramps are usually heavy and cumbersome, and several persons are usually called upon to manhandle the ramp into its storage position.
The prior art includes numerous ways in which the use of ramps, platforms, or gangplanks has been automated to allow a single person to position and store such a device. U.S. Pat. No. 4,011,615, issued to Maxson et al., discloses a bow gangplank that is intended for use on an offshore oil rig platform when violent wave action is present. It has a springloaded body that will elongate and shorten in accordance with wave inducements. The gangplank itself is not controllable from the boat but must be manipulated and maintained in position between the rig platform and docking vessel. However, it does feature a self adjusting feature that accommodates rough seas by extending and shortening the gangway to allow for movement of the ship during heavy seas. U.S. Pat. No. 4,293,967, issued to Ord, discloses a boat with a flip-over bow gangplank, wherein the gangplank in the stowed position is compactly maintained in trim against the bow form of the vessel. In docking, the gangplank is simply swung up and over to extend forward of the vessel onto a docking structure.
Other prior art stores the ramp or gangplank under the floor of the vehicle or boat. For example, U.S. Pat. No. 4,993,341, issued to Merkel, discloses an extendable gangplank for a pontoon boat, the gangplank being carried beneath the deck of the boat and extending outwardly under control of a DC motor. The extension mechanism consists of a combination of cables and pulleys which may be prone to jamming and interference by debris and other foreign matter in the water under the boat. The gangplank consists of a short portion and a long portion held together by hinges, so that when the long portion extends outwardly from the pontoon boat, the hinges will allow the long portion to drop from a horizontally extending position when the hinges extend over an outer supporting roller. No provision is made to slow the descent of the gangplank as it extends from the boat and this may present a danger to personnel on the shore.
U.S. Pat. No. 5,085,165, issued to Reed, also discloses another gangplank for a pontoon boat. The gangplank is pivotally connected to a guide section and is suspended from rollers below a deck of the boat between the pontoons. A central rib is provided along the underside of the gangplank, where the rib has two inclined portions joined at an apex with the portions riding on a fixed roller also mounted below the deck. When the gangplank is extended, the inclined portions function like a cam to lower the gangplank to a surface after the apex traverses the fixed roller, and when the gangplank is retracted, the gangplank is raised from the surface by cam action of the rollers. The gangplank is actuated by a cable having two ends connected to the guide section and powered by a winch.
U.S. Pat. No. 6,868,799, issued to Wright, discloses a ramp for a pontoon boat, where the ramp consists of a platform and a supporting structure for suspending the platform under a pontoon boat. The platform is supported on its distal end by a float and has a proximal end that is slidingly attached by blocks to a pair of parallel rails in the support structure. The apparatus has no rollers or a winching arrangement.
Each of these inventions provides an apparatus for extending and stowing a ramp or gangplank for a marine vehicle. Each becomes more complicated when an automated means for extending or retracting the gangplank is used. Furthermore, the clearance and space requirements of the apparatus, or its profile, is not particularly addressed in the prior art. Clearance is particularly important for land based vehicles such as trucks or vans, in order to maintain road clearance above the road surface. If the apparatus is mounted below the vehicle frame so that it extends toward the road surface, then it is prone to damage from road objects. Alternatively, if the apparatus is mounted above the vehicle frame, then the vehicle body may have to be raised to accommodate the apparatus. If this amount of elevation is excessive, then the center of gravity of the vehicle might change, resulting in a top heavy vehicle, which would therefore be less stable.
Thus as can be seen, there is a need for an improved extendable ramp apparatus that is simple, easily maintained, resistant to interference by debris or obstructions, and exhibits smooth operation. The apparatus should be lightweight so that it may be employed on a variety of vehicular platforms and corrosion resistant, particularly in a marine environment. It is desirable that the apparatus be as thin as possible in order to increase its utility for different vehicles. Finally, it is also desirable to prevent the ramp from rapidly dropping when it is extended so that people are not hurt and equipment is not damaged.